Protective helmet



FIG. 1 is a left side view of a protective helmet showing my new design;

FIG. 2 is a right side view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a perspective view thereof.

The details shown in broken lines in FIGS. 1-3 and 7 are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a protective helmet, as shown and described. 